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An Experimental Study on the Propagation of Impulse Noise in the Far Sound Field (원음장에서의 충격성 소음전파에 관한 실험적 연구)

  • 송화영;제현수;이주원;이성태;이동훈
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2004.05a
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    • pp.852-855
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    • 2004
  • This experimental study describes the propagation characteristics of the impulse noise emitted from the exit of a straight pipe attached to the open end of a simple shock tube. The sound pressure level and directivity of the impulse noise propagating from the exit of pipe with several different diameters are measured in the far sound fold for the range of the incident shock wave Mach number between 1.07 and 1.26. The experimental results showed that the peak values of impulse noises had a strong dependance on the exit diameter of a pipe and the shock wave Mach number. The impulse noise had the directivity propagating toward to the pipe axis and the characteristics of inverse square law of propagation distance. Moreover, it was shown that the one-third octave band SPL of impulse noise was almost constant regardless of the frequency band.

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A Strategy of Refrigerator Noise Control by Using Subjective Assessment (주관적 평가방법을 적용한 냉장고 소음대책 수립)

  • 정광일;김석관;이종구;김양한
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2001.11a
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    • pp.191-196
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    • 2001
  • The conventional methods for noise control attempts to simply reduce the level of product noise. This has been common practice in noise control industry. However, it is very straightforward common sense that we have consider human perception on noise. In this paper, we propose a noise control strategy which takes into account the subjective perception of product noise. We especially has concentrated on a refrigerator noise. The proposed method is composed of 3 steps. Firstly, the actual refrigerator noise signal is measured. Then, to make the sample noise set for subjective assessment the noise signal is edited in 1/3 octave bands. Finally, we establish a strategy of refrigerator noise control by using the results from subjective assessment of these noise signals

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Active Noise Control Using Wavelet Transform Domain Least Mean Square (웨이블릿 변환역 최소평균자승법을 이용한 능동 소음 제어)

  • Kim, Doh-Hyoung;Park, Young-Jin
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2000.06a
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    • pp.269-273
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    • 2000
  • This paper describes Active Noise Control (ANC) using Discrete Wavelet Transform (DWT) Domain Least Mean Square (LMS) Method. DWT-LMS is one of the transform domain input decorrelation LMS and improves the convergence speed of adaptive filter especially when the input signal is highly correlated. Conventional transform domain LMS's use Discrete Cosine Transform (DCT) because it offers linear band signal decomposition and fast transform algorithm. Wavelet transform can project the input signal into the several octave band subspace and offers more efficient sliding fast transform algorithm. In this paper, we propose Wavelet transform domain LMS algorithm and shows its performance is similar to DCT LMS in some cases using ANC simulation.

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A Study on the construction of Broad-Band Twisted-Wire Quadrature Hybrid (광대역 Twisted-Wire Quadrature Hybrid 회로구성에 관한 연구)

  • 박정기;김성진
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.17 no.6
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    • pp.78-85
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    • 1980
  • A symmetrical 3-dB quadrature hybrid circuits, consisting mainly of bifilar pair of taitoted wires, is described. A cascade of two such hybrid circuits can achieve an octave bandwidth hybrid circuit with a small coupling loss. Since the proposed type is simple, compact, and low In cost 1 its applicarion may be preferred to the more common coaxial line or printed -circuit type hybrid version in the frequency region below 1 GHz. This study provides a design method for a hybrid circuit mixing two different antenna signals for the anti - ghosting of television signal.

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A Study on the Noise Produced by Unsteady Exhaust Efflux of Engine (기관의 비정상 배기배출에 의해 생성되는 소음에 관한 연구)

  • 이민호;박명규
    • Journal of the Korean Society of Safety
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    • v.12 no.4
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    • pp.191-200
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    • 1997
  • This paper discusses prediction of the sound pressure level produced by simple engine exhaust systems(plain pipe, plain expansion chamber pipe, plain expansion chamber with internally extended inlet and outlet pipe, perforated pipe enclosed in a plain expansion chamber) and a computer program has been developed which predicts the sound pressure level and the frequency spectrum. The program utilizes unsteady flow gas dynamic theory and acoustic theory to predict the pressure-time history in the exhaust system and the mass flow rate-time history at the open end of the system and the sound pressure levels(1/3 Octave band levels) and the frequency spectrum in semi-anechoic room. The predictions are compared with measured levels and show a high degree of correlation.

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A Study on the Development of a Resonator to Reduce the Ship Engine Room Noise (선박기관실의 소음 저감을 위한 차폐공명기의 개발에 관한 연구)

  • Yu, Y.H.
    • Journal of Power System Engineering
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    • v.11 no.4
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    • pp.72-77
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    • 2007
  • It is known that elimination of ship engine room noise is impossible thing, so the working environment in the engine room is getting worse because ships are recently built with huge engines to take higher sailing power. In the yacht and cruise yacht, the engine room noise is more serious because they have bigger engines relative to their hull sizes. The noise generated from the main engine makes the employee to hearing loss and the transmitted noise make the uncomfortable conditions in the cabins of ship. The noise generated by ship engine must be attenuate for the employee and passenger. In yacht and cruise yacht, the noise levels in cabines are the most important criterions to the value of commodities. In this study, the noise absorbtion barrier which have resonators is experimentally studied by the 1/3 octave band noise elimination rates(%).

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Acoustic resonance by length of acoustic baffle at Finned Tube bank (핀-튜브군에서 배플 길이에 따른 음향공진)

  • 방경보;류제욱
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2003.11a
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    • pp.98-103
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    • 2003
  • This paper presents phenomena of vibration and noise due to acoustic resonance in tube bank of a HRSG. Acoustic resonance is may arise when the vortex shedding frequency coincides with the acoustic natural frequency. At this tube bank, dominant frequencies of vibration in this system were 43.5, 67.5㎐. The 3$\^$rd/ acoustic natural frequency calculated was 68.5㎐. When the difference of vortex shedding frequency and acoustic natural frequency is within ${\pm}$20%, acoustic resonance could occur. In this system, in order to prevent acoustic resonance, acoustic baffle was installed in the tube bank before operating. But acoustic resonance occurred. So, we evaluate the effect of acoustic mode due to baffle extension length. After investigating, we did revise acoustic baffle to eliminate acoustic resonance effectively.

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Korea Industrial Standardization Draft for ISO 354 (ISO 354 (잔향실법 흡음률 측정방법)의 KS 규격화)

  • Jung, Sung-Soo;Kook, Chan;Kim, Sun-Woo
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2003.11a
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    • pp.857-860
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    • 2003
  • We introduced the basic direction of revision for KS F 2805 (method for measurement of sound absorption coefficient in a reverberation room). It is fundamentally equal to ISO 354 (measurement of sound absorption in a reverberation room) which was state of ISO/FDIS 354. Two main points were strongly reviewed. First, the sound absorption coefficient values for Type J test specimen mounting was investigated. Next, the reverberation time difference between the conventional method and new additional one, impulse response method were compared.

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Prediction of Sound Radiation Power from Coupled Structures Uusing SEA (SEA법에 의한 결합구조물의 음향방사파워 예측)

  • 오재응;이명렬
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.1
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    • pp.20-28
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    • 1989
  • SEA(Statistical Energy Analysis) method has been applied to predict the sound radiation power from vibrating machinery. In this study, sound radiation power was predicted from coupled structures by transmission of vibration, which composed of two plates welded into an L shape. The predicted sound radiation power is in agreement within 2 or 3 dB on octave band comparing with values obtained from direct measurements. Also, in order to prove the validity of this method in changes of sound radiation power associated with modifications to structures, rubber pad was stuck on a plate. The results agree approximately within 3 or 5 dB. And SEA method is valuable for the optimal design to reduce the noise. Additionally, this paper suggests that the logarithmic decrement method is valid as the one for finding the loss factor.

An analysis of railway noise from comparison and evaluation between A-weighted SPL and sound quality indices (A-weighted 음압레벨과 음질 지수의 평가 및 비교를 통한 철도소음의 해석)

  • Kim, Dae-Sung;Wang, Se-Myung;Shin, Min-Cheol;Cho, Jun-Ho
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2006.05a
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    • pp.1459-1464
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    • 2006
  • In the previous studies on railway noise analysis, the main purpose of noise analysis is concerned with the reduction of A-weighted sound pressure level in order to satisfy noise regulations. However, more important facts on noise reduction are the subjective feelings of the human being on noise because people might be annoyed from the noise caused by train. In this paper, railway noise from different type of train are compared using the calculation of sound quality metrics with using strength related method that is calculation of A-weighted sound pressure level.

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